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Unit 9: Electricity

Adding or removing components — HIA International - Grade 8 Revision Notes & Topical Questions

5 min read 8 parts Lesson 6 of 12 2 quizzes

📚 HIA International - Grade 8 Hub / Topical Revision
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Lesson summary

Adding or removing components — HIA INTERNATIONAL notes: Predict how adding or removing cells and lamps changes the current and brightness in a series circuit.The current is the same all the way round a series circuit — electrons flow at the same speed in all the wires.Think of t…

  • Think of the electrons as a train
  • When the electrons start to flow in one part
  • An ammeter at any position gives the same reading
  • Cells and batteries are stores of chemical energy
  • Adding cells in series (the same way round)
  • Removing cells decreases the current

Section 1 of 8Current in a series circuit

1The current is the same all the way round a series circuit
  • The current is the same all the way round a series circuit electrons flow at the same speed in all the wires.
2Think of the electrons as a train
  • Think of the electrons as a train all parts of the train move at the same speed, and the back cannot go faster than the front.
3When the electrons start to flow in one part
  • When the electrons start to flow in one part they all start to flow.
4An ammeter at any position gives the same reading
  • An ammeter at any position gives the same reading and the components can be put in a different order without changing the current.

Section 2 of 8Adding or removing cells

1Cells and batteries are stores of chemical energy
  • Cells and batteries are stores of chemical energy they change it to electrical energy in a circuit.
2Adding cells in series (the same way round)
  • Adding cells in series (the same way round) gives more electrical energy, a larger voltage and a larger current, so lamps are brighter.
3
Two cells give double the current of one cell when the other components are identical.
4Removing cells decreases the current
  • Removing cells decreases the current when the other components are kept the same.
5A cell connected the wrong way round
  • A cell connected the wrong way round cancels the voltage of one cell.
6Too many cells can damage lamps
  • Too many cells can damage lamps and wires can get hot.

Section 3 of 8Adding or removing lamps

Adding or removing lamps
Lamps change electrical energy into light and thermal energy
  • Lamps change electrical energy into light and thermal energy electrons transfer energy to the lamp as they pass through.
Adding lamps in series
  • Adding lamps in series increases the total resistance, so the current decreases and every lamp is dimmer.
A circuit with two lamps transfers twice as much energy as one lamp, and the electrons move at half the speed.
Removing lamps increases the current
  • Removing lamps increases the current when the other components are kept the same.
Removing or breaking one lamp in a series circuit
  • Removing or breaking one lamp in a series circuit breaks the circuit, so all the lamps go out.

Section 4 of 8Other changes to a series circuit

Other changes to a series circuit
Adding a resistor or a longer wire in series
  • Adding a resistor or a longer wire in series increases the resistance and reduces the current.
A variable resistor
  • A variable resistor can control lamp brightness (a dimmer) or motor speed.
In series the supply voltage is shared
  • Vsupply = V1 + V2 + …

Section 5 of 8Comparison with parallel circuits

1Adding a lamp in a new branch of a parallel circuit
  • Adding a lamp in a new branch of a parallel circuit leaves the other lamps at the same brightness.
2The total current from the cell increases
  • The total current from the cell increases so the cell runs down faster.
3Removing a lamp from a parallel circuit
  • Removing a lamp from a parallel circuit leaves the other branches working.
4Houses are wired in parallel
  • Houses are wired in parallel so each appliance gets full voltage and can be switched independently.

Section 6 of 8Measuring current when components are added

1
Build a series circuit with a cell, a switch, a lamp and an ammeter.
2
Close the switch and record the current, then open the switch.
3
Add a second lamp and record the current, then a third lamp.
4
Repeat with one, two and three cells and the same lamp.
5
Display the results in a table or chart and write a conclusion.
6
Never remove all the lamps or connect an ammeter directly to cells; switch off at once if a lamp is too bright.

Section 7 of 8Key terms

TermMeaning
Series circuitA circuit with all components in one loop.
CellA store of chemical energy that provides electrical energy in a circuit.
DimmerLess bright.
ResistanceHow much a component opposes the flow of current.
VoltageA measure of the energy given to the charge by the supply.
Variable resistorA resistor whose resistance can be changed to control current.
Parallel circuitA circuit with branches.
AmmeterA meter that measures current.

Section 8 of 8Exam technique

1
Saying more lamps in series are brighter — they are dimmer because the current is smaller.
2
Saying current gets smaller after each lamp — it is the same everywhere in a series circuit.
3
Thinking a bulb breaking in series leaves the others on — all the lamps go out.
4
Adding cells the wrong way round — a reversed cell cancels the voltage of another.

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